System for recording electrical fluctuations



April 28, 1931. v. K. ZWORYKIN 1,802,747

SYSTEM FOR RECORDING ELECTRIC AL FLUCTUATIONS Filed April 12, 1927".Junnau WITNEI-ISSES: Y INVENTOR fig. My Y Wad/0117 ffiZworyk/h Y I Q aATTORNEY Patented Apr. 28, 1931 UNITED STATES PATENT orsica VLADIMIB K.ZWOBYKIN, OF SWISSVAIIE, PENNSYLVANIA, ASSIGNOR TO WESTING- HOUSEELEGIRIC 6a MANUFACTURING COMPANY, A. CORPORATION PENKSYL- 'VANIA.

SYSTEM FOR RECORDING ELECTRICAL FLUUIUATIONS Application filed April 12,

My invention relates to systems for recording electrical fluctuations,and in particular to systems wherein such fluctuations arephotographically recorded upon a light-sensitive, moving film. A

One object of my invention is to provide an improved device fortranslating electrical fluctuations into light-variations.

Another object of my invention is to provide a sound recording systemthat is substantially instantaneous in its response to electricalfluctuations representing sound frequencies.

Another object of my invention is to provide a sound recording systemwherein the record is undistorted.

Another object of my invention is to provide a sound recording systemwherein the intensity of the light from a constant source may be variedat frequencies corresponding to the highest harmonics accompanying vocalor instrumental music.

Still another and more specific object of my invention is to provide aKerr cell that is much more sensitive than Kerr cells known to the priorart. 7

There has arisen, in connection with television systems,photo-telegraphy, talking moving pictures, and the like, a very definiteneed for a device for translating voltage fluctuations into lightvariations. Such a device should refera ly have substantially no lag,should responsive to frequencies varying from those in the lowestaudible range to those lying in the so-called radiouency range, andshould also be capable of e ectively controlling light of arelativelyhigh intensity.

Numerous attempts have been made .to rovide a suitable translatingdevice of the c aracter described, amo which may be mentioned-the use ofmova le mirrors, the modu lation of a glow-tube, the use of themagnetooptic effect, and the use of Kerr cells.

Kerr cells of the prior art with which I am familiar, did not rmit ofthe control of a large amount of light at high intensity, for the reasonthat it was necessaryto very clowly space the two electrodes betweenwhich the light was transmitted. The space between and in sointercalatin 1927. Serial No. 183,226.

the electrodes varied from .3 millimeters to 1.5 millimeters, and theeffect of this spacing, together with the absorption in the nitrobenzeneor other dielectric in which the electrodes were immersed, acted to veryseriously limit the amount of light which could be effectivelycontrolled.

Kerr cells of the prior art were also undesirable as translating devicesby reason of the extremely high potentials which had to be impressedacross the electrodes. In an article by W. Schmidt in Annalen derPhysik, 17 page 142, 1902, among other data relative to Kerr cells as.then known, is given a formula which he states expresses the relationthat exists between the rotation of a beam of polarized light in 2. Kerrcell and certain other factors. Where B is a constant depending upon theliquid dielectric used, P, the applied potential, A, the distancebetween the electrodes, L, the length of the polarized light path thatis subjected to the electrostatic field, and D the rotation, the

formula reads as follows:

It is stated by Schmidt that when using electrodes separated a distanceof 1.5 mm. he was forced to employ potentials of the order of 15,000volts in order to obtain a satisfactory 1 tion, provided a Kerr cellthat operates with much lower potentials than cells of the rior art, andone that ermits the passage t erethrough of a muc larger proportion ofthe incident light than any of the cells heretofore known Specifically,my invention consists in subdividing each electrode of a Kerr cell intoa plurality of electrode elements,

these elements that the incident light is su jected to a plurality ofelectrostatic fields during its travel therebetween instead ofbeingksubjected to but a single field as in Kerr ce that were known. tothe prior art. In addition, I have provided a linear source of light andhave so correlated the sourceand the Kerr cell that each portion of thelight beam is subjected to a.

separate electrostatic field.

Among the features that I consider characteristic of my invention arethose set forth with particularity in the appended claims. The inventionitself, however, both as to its organization and its method ofoperation, together with further objects and advantages thereof, willbest be understood by reference to the following description, taken in,connection with the accompanying drawings, in which:

Figure 1 is a side elevational view of my improved Kerr cell;

Fig. 2 is a view, partly diagrammatic and partly perspective,illustrating a preferred form of electrical fluctuation recording systemutilizing my improved Kerr cell;

Fig. 3 is a fragmentary cross-sectional view of the cell itself, takenalong a line corresponding to the line 111 -111 of Fig. 1.

Referring to Figs. 1 and 3, my improved Kerr cell comprises a pluralityof glass plates 1 and 2, the surfaces of which are preferably opticallyplane and perfectly parallel. These plates are separated a very slightdistance by an element 3 analogous to a gasket, which is preferably madeof mica, glass or quartz. One of the plates supports thereon a pluralityof groups of electrode elements 4 and 5, the individual elements of theseveral groups being intercalated. The individual groups of electrodeelements are connected in parallel and they are provided with conductingelements 6 and 7 respectively which are preferably made of tin foil oranalogous material.

The plates 1 and 2 are held in assembled position, as shown in Fig. 3,by a suitable binding material 8 which is applied to the edges thereof.

The space 10 between the plates is filled with nitrobenzole or ananalogous dielectric material which causes rotation of plane polarizedlight when such light is passed therethrough and subjected to theinfluence of an electrostatic field between electrodes immersed therein.

Referring to Fig. 2, a complete recording system is indicated therein.The recording system comprises a linear source 11 of light, anachromatic condensing lens 12, a polarizer 13. a Kerr cell 14, ananalyzer 15,- a sec- 0nd lens 16, a screen element 17 provided with alinear opening 18 therethrough, and a light-sensitive medium, such as afilm 20.

The linear source 11 of light may be an incandescent lamp having asingle straight filament, or it may be a glow tube of any well-knowntype. The opening 18 through the screen element 17 is at right angles tothe path of travel of the light-sensitive medium and is parallel, orapproximately parallel, to the long axis of the light source.

The Kerr cell 14 is so arranged that the electrodes thereof are at anangle to the long axis of the light source. These electrodes arepreferably kept vertical, in order that any dust particles in the cellwill settle out and will not impede the passage of the lighttherethrough.

' The plane of polarization should be at 45 to the electrostatic field.

' In order that the operation of my improved system may be clearlyexplained, I have shown the electrodes of the Kerr cell connected acrossthe output circuit of a thermionic amplifier tube 30. The outputcircuit, in addition, comprises a potential source 31 and a resistor orreactor 32. The input circuit for the thermionic device coinprises thesecondary 33 of an audio frequency transformer 34, the primary 35 ofwhich may be connected in series with a microphone 36 and a voltagesource 37.

In order that the thermionic amplifying device shall operate upon thestraight por' tion of its characteristic curve, a source 38 of biasingpotential is incorporated in the grid circuit thereof. Potential changeson the grid thereof, therefore, are represented by amplified potentialfluctuations across the reactor 32 in the output, or plate circuit,which amplified fluctuations are a true copy, both as to frequency andrelative intensity, of the grid voltage fluctuations.

The potential changes across the reactor 32 are impressed on theelectrodes of the Kerr cell 14, and cause rotation of the plane ofpolarization of the light passing therethrough. The rotation varies asthe square of the applied potential, and the light which passes throughthe analyzer to affect the light-sensitive medium 20 accordingly bears avery definite relation to the excitation of the grid of the thermionicdevice.

It will be noted that the light from the linear source 11, after passingthrough the polarizer 13, falls on the electrodes of the Kerr cell in aline which is substantially at right angles to the direction in whichthe electrodes extend. Each individual pair of electrode-elementsaccordingly subjects a small portion of the light to the action of anelectrostatic field, in the same manner that the two electrodes of Kerrcells of the prior art affected the entire amount of light which wascaused to pass between them. The light from the source 11 isconsequently subjected to a rotational force which is many times moreeffective than if but a single pair of electrodes is employed, and, ifdesirable, a beam of light having a cross sect-ion substantially equalto the width of the cell may be employed to good advantage.

When using-a beam of large diameter such beam maybe of relatively lowintensity to obviate heating the nitrobenzole, and it may be reduced toan appropriate size for recording by an appropriate lens system.

The microphone 36 is shown merely as indicative of a source ofelectrical fluctuations and it may obviously be replaced by any otherequivalent device. The system may, for example, be utilized for thephotographic recording of either radio or telegraphic signals, or it maybe utilized in television or picture telegraphy systems.

There are two methods for preparing the thin glass plate which carriesthe electrode systems; one of these methods comprises plating the glasswith a metal having good conductivity and then removing certain portionsof the metal in order to form the two electrode systems. The othermethod comprises ruling the glass with two systems of parallel lines,each group being connected by a groove extending at right angles to themain grooves and then rolling a metal, such as silver or copper, intoall of the grooves. The lines are ruled quite close together, thepreferred spacing being one one-hundreth of a millimeter or less, andthe resulting space between the metallic electrode elements isapproximately one-half of this amount.

The unruled space between the electrode elements is, of course,transparent to light, and a plurality of such plates may be arrangedserially in such manner that the lines and the spaces of the severalplates are aligned, in order to construct a modified form of cell.

The space 10 between the two glass plates illustrated in Fig. 3 ispreferably of the same order of magnitude as the space betweenindividual electrode elements. In other words, if the electrode elementsare separated by five thousandths of a millimeter, this same space isamply sutficient between the two glass plates, it onl being necessarythat the nitrobenzole shall be able to penetrate therebetween and coverall of the said electrode elements.

The various figures of the drawings are not drawn to scale, but therelative proportions are exaggerated in order that the details of myimproved cell may be apparent. In an actual embodiment of my inventionthe glass plates 1 and 2 have a thickness of not more than a fewmillimeters, and, as before explained, they are preferably separated bya space of the order of five thousandths of a millimeter.

- preciable thickness,

Each individual electrode element is'made so thin that the entireassembly casts an inappreciable shadowwhen interposed between a sourceof light and a screen.

Insofar as I am aware, a. Kerr cell of-this type has not heretoforebeenmade, the cells with which 'I am familiar compr sing only twoelectrodes. each electrode having an apfluct'uations, a linear sourcebetween which a beam of light of high intensity was caused to pass. Suchcells were unsatisfactory by reason of the fact that in order to obtainsuflicient light for recording purposes it was unnecessary to use ahighly concentrated beam which tended to heat the nitrobenzole and causechemical action therein.

My improved cell is principally advantageous in that it permits of theuse of voltage much lower than those heretofore employed. It is alsoapparent, from an inspection of the formula previously given, thatinasmuch as the rotation is inversely proportional to the square of thedistance between the elec trodes, my improved cell will permit of muchmore eflicient control of a light beam than cells of the prior art inwhich the electrodes were separated by distances of the order of threetenths to one and' one-half millimeters.

My improved cellis also much more sensitive than cells with which I havepreviously been acquainted, the sensitivity being proportional to thesquare of the distance between adjacent electrode elements. My improvedsystem operates with substantially no lag and as a consequence the lightfaithfully represents the signal frequencies which are being recorded.This feature is of very considerable advantage in connection with themaking of talking motion picture films.

AlthoughI have illustrated and described only one form which myinvention may take. it is obvious that many modifications thereof arepossible. The invention therefore, is not to be limited except insofaras is necessitated by the prior art andby the spirit of the appendedclaims.

I claim as my invention:

1. In a system for recording electrical fluctuations, a linear. sourceof light, a lightsensitive medium, a Kerr cell comprising a plurality oflinear electrodes interposed between said source and said medium, andmeans for impressing electric potentials across said electrodes.

2. In a system for recording electrical of light, a lightsensitivemedium, a Kerr cell comprising n plurality of groups of linearelectrodes interposed between said source and said medium, means forolarizing said light before it reaches said err cell, and means foranalyzing said light interposed between said Kerr cell and sa1dlight-sensitive medium.

3. In a "system for recording electrical fluctuations, a linear sourceof light, a lightsensitive medium, a Kerr cell comprising a plurality ofgroups of linear electrodes interposed between said light and saidmedium, the electrodes of the individual groups being connected inparallel and means for impressing electrical potentials on said grougiofelectrodes.

I 4. a system for recording electrical fluctuations, a linear lightsource, a lightsensitive medium, a Kerr cell comprising.) a plurality oflinear electrodes interposed etween said source and said medium, and ascreen having a linear opening interposed between said Kerr cell andsaid medium, the opening and the light source being approximatelyparallel and the said electrodes extending at an angle thereto, wherebymore than two electrodes are effective in controlling the light whichpasses from said source to said medium.

5. In a system for recording electrical fluctuations, a linear source oflight, a Kerr cell comprising a plurality of substantially parallellinear electrodes, and means whereby the light from said source falls onsaid electrodes in a beam transverse thereof.

In testimony whereof, I have hereunto subscribed my name this 9th day ofApril, 1927.

VLADIMIR K. ZWORYKIN.

